This invention relates to an improved process for the manufacture of chloroprene and particularly to an improved method of recovering it from the crude reactor effluent.
Chloroprene (2-chlorobutadiene-1,3) is an important monomer used in the manufacture of a number of synthetic elastomers. This monomer is normally made by dehydrochlorination of 3,4-dichlorobutene-1 (sometimes hereafter abbreviated to DCB) with an aqueous alkali such as sodium hydroxide. U.S. Pat. No. 3,981,937 to Campbell et al. discloses a catalytic process for carrying out this dehydrochlorination. The catalyst usually is a quaternary ammonium chloride but can also be another quaternary ammonium compound.
In one of the variants of the Campbell et al. process DCB, aqueous alkali, and the catalyst are introduced into one or more agitated reactors and are allowed to react at a moderately elevated temperature (say, 50.degree.-70.degree. C.) until DCB is substantially completely dehydrochlorinated. The process is normally carried out in a continuous manner since the catalyst permits high conversions at moderate temperatures and short residence times. The reactor effluent contains the chloroprene product, excess aqueous alkali, brine formed in the process, the catalyst, a minor amount of chloroprene isomer (1-chlorobutadiene), and high boiling organic materials including various polymers of chloroprene and of 1-chlorobutadiene. Chloroprene is recovered from this effluent by steam-stripping, and the remaining material is separated in a decanter into the aqueous phase and the organic phase. The latter is incinerated or otherwise disposed of; the former is pumped into deep wells following a pH adjustment and other treatment.
Valuable catalyst is lost in this recovery process because of deactivation under alkaline conditions at the steam-stripping temperature (about 90.degree.-95.degree. C.), which makes catalyst recovery impractical. Catalyst residues are present in the high-boiling organic phase which is incinerated. In addition to this loss, considerable energy is wasted because of the high heat input requirement in the steam-stripping step.
It thus would be highly desirable to improve the efficiency of chloroprene recovery in the catalytic process for its manufacture, reducing the catalyst loss and improving the energy utilization.